This invention relates to improvements in ink agitators for printing machines, and more specifically to ink agitators which are driven back and forth across the ink fountain to homogenize the ink therein.
Conventional printing machines include an ink fountain or reservoir extending across the width of the machine at a position near the top thereof. The ink fountain is periodically or continuously supplied with ink. The ink is eventually removed from the ink fountain by a fountain roll, then transferred by means of one or more duct rolls, transfer rolls, and vibrating rolls to a printing plate cylinder or blanket cylinder which actually transfers the ink onto the media for which it is intended. Different inks are formed of different chemical compositions. Some chemical compositions react with air in such a manner as to adversely affect the subsequent printing operation. For example, some inks will form a surface skin unless the ink is continuously stirred or mixed. Other inks must be continuously stirred in order to maintain the color consistency. This is referred to as keeping the ink "open."
It has therefore become recognized in the printing industry that it is highly desirable to maintain the ink in the ink fountain homogenized by agitation or stirring. Early ink agitators were driven by means of a motor attached to the frame of the printing machine and coupled to the stirring device or agitator by some type of transmission means such as belts, chains or the like. While such arrangement is preferable to manual stirring or no agitation at all, it is relatively ineffective as far as being completely satisfactory is concerned. The ink tends to collect on the chains, belts, and the like causing continuous maintenance problems. Further, such equipment is cumbersome and expensive. A further advance is shown in U.S. Pat. No. 4,108,068, issued Aug. 22, 1978 in which a self-driven mobile assembly is supported parallel to the longitudinal axis of the ink fountain on a beam extending thereacross. While such ink agitators offered some improvement, they are still not completely satisfactory of down time and excessive maintenance problems.
A further approach which eliminates electric motors and chain drives utilizes linear drive cylinders such as hydraulic or pneumatic cylinders. However, conventional linear drive cylinders are not applicable in this situation, because here there is not sufficient room to mount the drive cylinder and still allow the piston rod to traverse the entire width of the printing machine. Rodless, linear drive cylinders in which a pneumatic piston within the sealed hollow tube is moved backwardly and forwardly by air or fluid are appropriate. However, as applied to ink agitators, the only known use of such types of rodless, linear drive cylinders are those in which the carriage carrying the ink agitator is connected to the piston within a hollow tube of special cross-sectional shape by means of a sliding seal along an open side of the cylinder. Such types of ink agitators are manufactured by Grafische Technik GmBH of Augsburg, West Germany, and offered for sale in this country under the trademark "PIAC." The sliding seal carriage is relatively expensive, difficult to maintain, and still suffers from the possibility of ink, oil, grease, and dust leakage into the cylinder.
Therefore, in the present invention, the carriage which carries the agitator is magnetically coupled to the piston of a rodless, linear drive cylinder rather than being mechanically coupled thereto. This approach is considerably less expensive and more effective in that leakage of contaminants into the cylinder is impossible.
Toward this end, a cylindrical hollow tube, sealed at the ends, is mounted to the printing machine to extend longitudinally of the ink fountain. The hollow tube is filled with a working fluid and includes a piston slidably positioned therein for reciprocating movement back and forth within the hollow tube responsive to the flow of the working fluid into the ends thereof. A yoke or carriage surrounds the hollow tube and is magnetically coupled to the piston therein, whereby movement of the piston induces a similar movement of the yoke, even though the yoke and piston are not mechanically attached. Therefore, the carriage is driven back and forth by the piston without any slot in the sealed tube. By such approach, it is impossible for any ink, grease, or dust to leak into the pneumatic tube to create maintenance problems.
An agitator is connected to the carriage and suspended in the fountain whereby movement of the yoke causes movement of the agitator through the ink fountain.
Several further developments serve to improve the appratus and minimize maintenance even further. Such further improvements include a protective housing or cover surrounding, substantially encasing the drive cylinder and carriage on three sides, which housing carries the drive cylinder and is hingedly attached to the sides of the printing machine; a unique bearing and pinion connecting the agitator carriage to a geared rack which ensures constant even mesh of the pinion with the rack throughout the reciprocating movement during operation; means for quickly removing the agitator from the carriage for cleaning purposes; and a housing support bracket so constructed that the entire agitator apparatus is quickly and easily removable from the machine for replacement purposes.
It is therefore one object of the present invention to provide an improved ink agitator which is simple, easily replaceable, and substantially free from maintenance problems.
It is another object of the present invention to provide an ink agitator of the type described which utilizes a rodless, linear drive cylinder in which the agitator carriage is magnetically coupled to the interior drive piston, thus eliminating any opportunity for ink, grease, or dust to leak into the pneumatic cylinder.
Another object of the present invention is to provide an ink agitator of the type described which includes a drive pinion maintained in positive engagement with the teeth of a drive rack by means of a complementary bearing.